Liquid propellants, solid propellants, and gelled propellants have been developed to high levels of performance. Each of the propellant types has been preferred for a specific use. Solid propellant propulsion has been widely used by the military services as evidenced by the many well known solid rocket systems. Solid propellants have been employed in many well known systems having a large variation in sizes from very small to extremely large rocket motors. Solid propellant composition developmental programs specifically devoted to solid binder ingredients, oxidizing salts both organic and inorganic, plasticizers, stabilizers, burning rate modifiers and catalysts, curing agents, processing aids and metal fuel additives in advancing the state-of-the-art. Further discussions relating to solid propellant classification groups are set forth hereinbelow since solid propellants have dominated the propulsion field over the years.
Solid propellants are generally classified into two groups: homogeneous propellants and composite propellants. Composite propellants consist of propellants wherein solid oxidizers and other solid additives are dispersed within an organic binder such as polybutadiene-acrylic acid polymers, polysulfide polymer, polyester heteropolymerized with unsaturated olefins, and polyurethanes. The homogenous propellant consists of gel type propellants of single, double, and triple base type. Double-base propellants containing nitrocellulose, a plasticizer, metal fuel, inorganic oxidizer, stabilizers, processing aid, cross-linking agent, and burning rate catalyst have been particularly attractive because of the high burning rates and stabilities thereof.
Gelled propellant fuel such as a thixotropic rocket fuel comprised of monomethylhydrazine, metallic fuel particles, dimethylurea, and a gellant is disclosed in U.S. Pat. No. 4,039,360 for an invention issued to Barry D. Allan on Aug. 2, 1977. This thixotropic fuel gel has the ability even with low gellant concentration to maintain metallic fuel particles dispersed therein even under several hundred g's loading. For applications where fuel tank volume is limited, it is desirable to increase the density of the fuel (by adding metallic fuel particles) while maintaining a high specific impulse.
The combination of liquid gel fuel and liquid gelled oxidizers have been employed in hypergolic propulsion system. A well known oxidizer gel is inhibited red fuming nitric acid gel (IRFNA GEL). This oxidizer gel has also been employed with a gel/solid bipropellant propulsion system. A gel/solid bipropellant propulsion system is also known as a hybrid system. A gel/solid bipropellant propulsion system with energy management capability as disclosed in U.S. Pat. No. 5,133,183 for an invention issued to Asaoka, Chew and May on Jul. 28, 1992 is commonly assigned to the United States of America as represented by the Secretary of the Army, Washington, D.C. Leo Asaoka, and Douglas L. May and William M. Chew are joint inventors who are also joint inventors of the present invention. The propulsion system of U.S. Pat. No. 5,133,183 employs a solid fuel gas generator to furnish fuel-rich combustion gases which serves as the pressurization source to expel IRFNA gel and also serves as a fuel for hypergolic reaction with the simultaneously injected IRFNA gel in a combustion chamber.
A solid fuel ducted rocket with gel-oxidizer augmentation propulsion is disclosed in U.S. Pat. No. 5,152,136, issued on Oct. 6, 1992 to Chew et al and commonly assigned to the United States of America as represented by the Secretary of the Army, Washington, D.C. This system employs a solid fuel gas generator (SFGG) in combination with IRFNA gel for higher thrust in a boost or dash stage of a flight. The air ducts of the ducted member scoop air in from the atmosphere for hypergolic reaction with fuel-rich hot gases during a sustain stage of a flight.
The above patents issued to Asaoka et al and Chew et al describe approaches for achieving on-demand, variable thrust performances wherein the variable thrust results in a cost to propellant usage efficiency. The use of multiple liquid or gel engines, which can be turned on and off in various combinations to provide incrementally variable thrust results in additional costs in addition to lower propellant usage efficiency as a result of multiple combinations which are significantly higher in total cost.
The present requirements for tactical rocket motor and rocket engines having acceptable minimum signature rocket plume signatures and which have essentially inherent insensitive munition (IM) properties, have influenced the development of an additive for fuel gels and solid fuel-gas generators. Such an additive when considered for use with the systems described hereinabove and which meet the present requirements for tactical missile would be a desirable achievement in its field of use with the recognized advantages set forth hereinbelow.
An advantage of gel, hybrid, and ducted rocket fuels is that they can be loaded with solid high energy materials that increase both specific impulse, lsp, and density impulse .rho.*lsp. Gel bipropulsion, hybrid, and ducted rockets have separate fuel and oxidizer supply systems that cannot interact unless injected into the combustion chamber. The systems, therefore, have essentially inherent insensitive munition (IM) properties. Solid propellants can not make efficient use of solid fuel additives because they are already fuel rich: if additional solids could be incorporated into them, then solid oxidizers are preferred. Gel propulsion systems have used fuel gels containing aluminum and carbon, whereas solid fuel-gas generators have been used with carbon and hydrocarbons as additives.
Several solid materials, such as aluminum and boron, have been used as solid fuels in propulsion systems; however, rocket plume signatures of these materials are unacceptable. With a few exceptions, the Army prefers propulsion systems with minimum signature to decrease launch point detection and increase survivability, to minimize interference with seekers and communications in the battle field, and to increase kill probability.
An objective of this invention is to provide a high energy additive for solid fuel-gas generators applicable to gas-gelled oxidizer hybrid rockets.
Another object of this invention is to provide a solid additive for solid fuels employed in solid-fuel-gas generators applicable for ducted rockets.
A further object of this invention is to provide a solid fuel for addition to a solid fuel gas generator during formulation to improve physical properties, and good ejection efficiency during combustion of the solid fuel gas generators to produce fuel-rich hot gases for further combusting in a combustion chamber of a solid fuel ducted rockets and fuel gas-gelled oxidizer hydrid rockets.
Still a further object of this invention is to provide a minimum signature solid loading for a fuel gel to replace metal and carbon in hybrid loaded fuel gels whereby the density specific impulse (.rho.*lsp) is higher than that of the carbon loaded fuel gel.